Engine air flow may be controlled via a central or primary throttle that regulates air flow from an air filter of an engine air intake into an engine intake manifold and engine cylinders. The throttle may include an electric actuator, such as a motor, to regulate a position of a throttle plate of a butterfly valve. The position of the throttle may be based on a position of an accelerator pedal and vehicle speed. In particular, the accelerator pedal position may be converted into a driver demand torque and the driver demand torque is converted into an engine air flow amount and a fuel flow amount that provides the driver demand torque. However, if the vehicle in which the engine operates is driven to higher altitudes where barometric pressure is lower than at sea level, engine torque may not meet driver demand torque because air is less dense at higher altitudes and because the engine air intake may restrict the less dense air from entering the engine. Further, if an engine air intake filter upstream of the throttle is partially obstructed by debris, engine performance may be reduced more than is desired at low altitudes.
The inventor herein has recognized the above-mentioned limitations and has developed an engine control method, comprising: opening a fuel vapor storage canister vent valve and closing a fuel tank vapor blocking valve via a controller in response to an indication of barometric pressure less than a first threshold and a driver demand torque greater than a second threshold.
By adjusting operating states of devices in a fuel vapor control system, it may be possible to provide the technical result of improving engine air flow at higher altitudes where barometric pressure is lower so that engine performance degradation may be reduced. For example, a fuel tank vapor blocking valve may be closed and the fuel vapor storage canister vent valve may be opened to prevent fuel vapors from flowing to the engine while air flows to the engine via a passage leading from atmosphere through a fuel vapor storage canister and to the engine intake manifold. Further, air may continue to flow into the engine via a throttle. Thus, an additional air passage into the engine that may be less restrictive, may improve air flow into the engine at higher engine loads. Further, a canister purge valve may be operated proportionately to accelerator pedal position during conditions when an air filter of the engine is partially cogged and in a degraded state.
The present description may provide several advantages. Specifically, the approach may provide improved vehicle drivability during conditions of low barometric pressure.
Additionally, the approach also includes for increasing engine air flow during some conditions when an air filter is degraded so that driver demand torque may be more closely followed. Further, the approach may be performed without need for additional engine hardware.
The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings.
It should be understood that the summary above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure.